《化工热力学》课程授课教案（讲义）Chapter 7 Application of Thermodynamics to Flow Processes

Chapter 7 Application of Thermodynamics to Flow Processes Review For a steady-state flow process M+答+g=0+形 名-2a8-2增a (∑B)n=(∑B)+D 7.1 Duct Flow of Compressible Fluid 7.2 Turbines(expanders) 7.3 Compression Processes 7.1 Duct Flow of Compressible Fluid 2+84=Q+m H145 H3u,2, △H=0orH2=H hrottling Processoccurs at constant enthalpy Thinking(7-1) (1)throttlingprocess for idealgas T1 T2? (2)throttling process for wet steam Cause the liquid to evaporateand the vaporto become superheated

Chapter 7 Application of Thermodynamics to Flow Processes Review For a steady-state flow process 2 2 s u H g z Q W   + +  = + , j j j i i G j i j j Q m S m S S T     − − =   ( ) ( )   B B D in out = + 7.1 Duct Flow of Compressible Fluid 7.2 Turbines (expanders) 7.3 Compression Processes 7.1 Duct Flow of Compressible Fluid 2 2 u H g z Q W   + +  = + hrottling Process occurs at constant enthalpy Thinking(7-1) (1) throttling process for ideal gas T1、T2? (2) throttling process for wet steam Cause the liquid to evaporate and the vapor to become superheated 2 1  = = H or H H 0 1 1 1 1 1 P T H u z 2 2 2 2 2 P T H u z

(3)throttlingprocess for saturatedliquid Some ofliquid vaporizes or flashes 7.1.1 Throttling Process Joule-Thomsoncoefficient - 微分节流效应系数，有时用山，表示 节流过程中压力变化所引起的温度变化： A=T,-I=∫udP Joule-Thomson coefficient ())()- (》=c ,- 别 部-().（〔） ,-r- V=ZRT/P

(3) throttling process for saturated liquid Some of liquid vaporizes or flashes 7.1.1 Throttling Process Joule-Thomson coefficient H s T P     =      微分节流效应系数,有时用 J 表示 节流过程中压力变化所引起的温度变化： 2 1 2 1 d P H P  = − = T T T P   Joule-Thomson coefficient 1 y x F F x y x y F                = −         P P H C T      =    T P H V V T P T           = −       H T P     =      H P T T T H P H P                = −          1 P T H H T P −       = −          T P H V V T P T           = −       V ZRT P = /

),-( “=部) u For ideal gas 21-0 For real gas 某种气体的节流效应可以通过实验确定在某一高压状态P1,T1, 向不同P2进行节流膨胀，同时可测得此时的2，描点画图，可得出 一系列等焓线。等焓线上任一点的斜率值即为μ值。 H0 Constant enthalpy curve 0 Joule-Thomson inversion curve P Inversion curves for reduced coordinates Thinking(7-2) Application ofthermodynamics to other flow processes

2 T P H Z RT P P T           = −       1 P T H C P     = −      2 P P RT Z C P T     =      For ideal gas 2 1 0 P P RT Z Z C P T     = = =      For real gas 某种气体的节流效应可以通过实验确定.在某一高压状态 P1，T1， 向不同 P2 进行节流膨胀，同时可测得此时的 T2，描点画图，可得出 一系列等焓线。等焓线上任一点的斜率值即为 μ 值。 Thinking(7-2) Application of thermodynamics to other flow processes  = 0 Joule-Thomson inversion curve   0   0 P T Constant enthalpy curve Inversion point Inversion curves for reduced coordinates Pr Tr   0   0

4H+4n +g△=Q+W 2 (2)Nozzle and Diffuser Diffu Nozzle 喷嘴与扩压管的结构特点是进出口截面积变化很大。流体通过 时，使压力沿着流动方向降低，而使流速加快的部件称为喷嘴。反之， 使流体流速减缓，压力升高的部件称为扩压管。 Thinking(7-2) :+g=Q+ AH+-0 2 A,-H=-蓝 流体通过焓值的改变来换取动能的调整 2 7.2 Turbines(expanders) 7.2.1 Reversible Adiabatic Expansion(可逆绝热膨胀) 容-号- d

2 2 s u H g z Q W   + +  = +  = H Q (2) Nozzle and Diffuser 喷嘴与扩压管的结构特点是进出口截面积变化很大。流体通过 时，使压力沿着流动方向降低，而使流速加快的部件称为喷嘴。反之， 使流体流速减缓，压力升高的部件称为扩压管。 Thinking(7-2) 2 2 s u H g z Q W   + +  = + 2 0 2 u H   + = 2 2 1 2 2 1 2 u u H H − − = 流体通过焓值的改变来换取动能的调整 7.2 Turbines (expanders) 7.2.1 Reversible Adiabatic Expansion（可逆绝热膨胀） , ( ) ( ) CV j fs G j j d mS Q mS S dt T  + − =  Nozzle Diffuser

△(mS)6=0 Because of△(mS)s=∑m,S,-∑m,S S0∑ms=∑m5,orAS=0 Isentropicprocess 微分等熵效应系数 4-( %) 4>0 制冷效应 任何气体在任何条件下，进行等熵膨胀，气体温度必定降低 节流过程中压力变化所引起的温度变化： △T=T2-T=∫4dP 7.2.2 Principle of Turbines(expanders) A turbines (expanders)consists of alternate sets of nozzles and T,P rotating blades 2 T2,P2

( ) 0  = mS fs Because of ( )fs j j i i j i  = − mS m S m S   So i i j j i j   m S m S = or  = S 0 Isentropic process 微分等熵效应系数 S S T P     =      S P P T V C T     =      0 S  制冷效应 任何气体在任何条件下，进行等熵膨胀，气体温度必定降低 节流过程中压力变化所引起的温度变化： 2 1 2 1 d P S S P  = − = T T T P   7.2.2 Principle of Turbines (expanders) A turbines (expanders) consists of alternate sets of nozzles and rotating blades 1 2 T2， P2 T1, P1 Ws

透平机是借助流体的减压和降温过程来产出功 Steady-state flow through a turbine or expander 7.2.3 Energy balance for Turbines(expanders) 兰+g=Q+ W=△H=H2-H, or市=m△H=iH2-H) 7.2.4 Calculation for Turbines (expanders) Normally,T1,P1,P2 are known How to calculate Ws? W,=△H=H2-H Review For a purespecies,the freedom degree F=? Normally,T1,P1,P2 are known How to calculate Ws? W=△H=H2-H Tl.PI H1→H2? If the fluid in the trbine undergoes an expansion process that is reversible as well as adiabaticto state 2

透平机是借助流体的减压和降温过程来产出功 Steady-state flow through a turbine or expander 7.2.3 Energy balance for Turbines (expanders) 2 2 s u H g z Q W   + +  = + W H H H s =  = −2 1 2 1 or ( ) W m H m H H s =  = − 7.2.4 Calculation for Turbines (expanders) Normally, T1, P1, P2 are known How to calculate Ws? W H H H s =  = −2 1 Review For a pure species, the freedom degree F=? Normally, T1, P1, P2 are known How to calculate Ws？ W H H H s =  = −2 1 T1, P1 H1 H2 ? If the fluid in the turbine undergoes an expansion process that is reversible as well as adiabatic to state 2′ 1 2 T2， P2 T1, P1 Ws

S=S: S0S,B→Hg T1,P1→S1,H1 S=Sg→H W.(isentropic)=HH=(AH), H Actual expansion process irreversible Ws (isentropic)>Ws (actual) (△H =△H Define the turbine efficiency W. AH (isentropie)(A)s Example 7.6 Solution7.6 TI,P1,P2,n are known Clue: nP1→HS1 S,=S3 SB→H: W.(isentropic)=HH=(AH), H→ (AH)s AH H,=AH+HH =AH+H →m

1 2 S S =  So S ,  2 2 P H2  T1, P1 S1, H1 1 2 S S =  H2  s 2 1 (isentropic) ( ) W H H H s = − =   Actual expansion process is irreversible Ws (isentropic) ＞ Ws (actual) =△H Define the turbine efficiency: ( ) ( ) s s S W H W isentropic H    =  Example 7.6 Solution 7.6 T1, P1, P2,η are known Clue: T1 P1 H1 S1 1 2 S S =  2 2 S P H2  s 2 1 (isentropic) ( ) W H H H s = − =   ( )S H H   =  H H H H 2 1 =  + H H H 2 1 =  + m P2 P1 H 1 2′ △H 2 (△H)s

7.3 Compression Processes 7.3.2 Energy Requirements of Compressor Equipment with rotating blades or In cylinders with reciprocating pistons W,=△H For adiabatic reversible compression 个H process W,=(△H) △H P (△Hs .(isentropie)(H) △H

7.3 Compression Processes 7.3.2 Energy Requirements of Compressor Equipment with rotating blades or In cylinders with reciprocating pistons 2 2 s u H g z Q W   + +  = + W H s =  For adiabatic reversible compression process W H s s =  （ ） Compressor efficiency ( ) ( ) s S s W isentropic H W H    =  P2 P1 H S 1 2′ △H 2 (△H)s T2 T1, P1 Ws